360 Organic waste recycling: technology and management
of treatment would be necessary during the periods when the aquatic system is
not functional.
Rain
Rain storms could overload aquatic systems hydraulically. Water inflow will
increase from I/I (inflow/infiltration) and direct rainfall into the APU's. Direct
rainfall alone from a typical storm could more than double the hydraulic load to
an aquatic system. The nature, magnitude, and duration of effects resulting from
hydraulic overloading are unknown. Probable effects of hydraulic overloading
would include wash-through of BOD 5 , re-suspension of sediment, and addition
of dissolved oxygen to APU's designed to be anaerobic.
Table 7.8 Calculated value of the rate coefficient, k as a function of hydraulic application
rate (Weber and Tchobanoglous 1986)
Hydraulic application rates (m^3 /m^2 -day) k (mg/L-day)
9.91 11.9
14.8 9.47
19.9 8.77
Note: k =hydraulic application rate multiplied by the slopes from Figure 7.17
Wind
Wind can alter the aquatic environment directly or indirectly, the latter by
damaging the plants. Wind increases the rate of gas transfer between the
wastewater and atmosphere. Wind also increases water turbulence, which may
result in re-suspension of sediment. Plants broken or otherwise damaged by
wind may not function as intended, which would upset the wastewater treatment
process until the plants have recovered. Floating plants, particularly duckweeds,
are more sensitive to wind than rooted plants because the former tend to be
blown around and may result in open water surfaces which are vulnerable to the
direct effects of wind and other environmental factors. Though more sensitive to
winds, floating plants, by virtue of their mobility, are less likely to be physically
damaged by wind than rooted plants.
Environmental factors
Environmental impacts that could result from the presence of an aquatic
treatment system include odors, fog generation, increased vector-organism
population, and introduction of nuisance organisms to the local environment.
The potential for significant environmental impact from any of these or other
factors must be evaluated and mitigating measures taken as necessary.